Charge pump circuits are widely used in integrated circuits to provide a direct current (DC) voltage higher than a specified supply voltage. The charge pump circuit is generally controlled by clock signals of opposite phase supplied by an oscillator. For high voltage applications, the output voltage may be regulated referring to the supply voltage, and then be used to drive external or integrated N-type power MOS transistors or other suitable electronic devices.
The voltage difference between the output voltage and the supply voltage is generally determined by one or more zener diodes with or without a resistor in series. However, the voltage difference may be inaccurate due to the manufacturing deviations in integrated circuits. Moreover, a large spread could be introduced into the output voltage of the charge pump circuit, which may adversely affect the accuracy of the voltage difference between the output voltage and the supply voltage as well.